1. Field of the Invention
The present invention relates to a water-dispersible blocked isocyanate composition, a water-base paint (or distemper) composition and a water-base adhesive composition mainly containing a water-base (or aqueous) resin.
2. Related Background Art
Heretofore, there have widely been used various paints, adhesives, and coating materials containing an organic solvent having a good power to dissolve a polymer. However, the organic solvent contained in these paints, etc., can cause various problems such as adverse effect on a human organism, safety or hygiene problems inclusive of explosion, fire hazard, etc., and pollution problems inclusive of air pollution.
Accordingly, in recent years, in order to solve the above-mentioned problems caused by the use of the organic solvent, there have actively been developed paints, etc., of a "water-base" system using substantially no organic solvent.
In the water-base system, there has heretofore been used a water-base resin such as aqueous solution of a water-soluble polymer, and aqueous dispersion, aqueous emulsion, or aqueous suspension which have been obtained by dispersing a water-dispersible polymer in water. However, in many cases, such a water-base system (one-liquid or one-component system) only using the above water-base resin cannot provide various properties which are required for the above paint, etc. Therefore, in general, a crosslinking agent is used in combination with the water-base resin for the purpose of improving the resultant weather resistance, adhesion property, etc.
As an example using such a crosslinking agent, there is known a system (two-liquid or two-component system) using a curing agent (or hardening agent) having a free isocyanate group, in combination with the above-mentioned water-base resin. However, the two-liquid system has a limitation such that it only has a short work life (or pot life) after the mixing of the curing agent with the above polymer component, and therefore this system has a problem in view of the workability or usability thereof.
As an example the measure for alleviating the above defect of the two-liquid system, there is known a method of using a water-dispersible blocked isocyanate as the above-mentioned crosslinking agent. This is a system wherein a paint, etc., is heated at the time of the use thereof to dissociate the blocking agent and regenerate the free isocyanate, and then the resultant isocyanate is caused to react with an active hydrogen group of the polymer component constituting the water-base resin to convert the polymer into a network structure. In the system using such a water-dispersible blocked isocyanate, since the isocyanate group is blocked, the work life of the system is not limited, unlike in the case of the two-liquid system using the free isocyanate.
As specific examples of the system using the water-dispersible blocked isocyanate, those as described in Japanese Laid-Open Patent Application Nos. Sho 61-31422 (i.e., 31422/1986) and Hei 4-159260 (i.e., 159260/1992) are known. A hydrophilic surfactant has been introduced into the blocked isocyanate used in these references, for the purpose of improving the dispersion stability thereof at the time at which the blocked isocyanate is mixed with an aqueous solution of a water-soluble polymer or a water-base emulsion.
In recent years, the requirement for the resultant product of a paint, etc., becomes severer, and therefore the requirement for the appearance of a (dry) paint film (especially, gloss and definition or sharpness) also becomes severer. In such a viewpoint, there has been desired a further improvement in the performance of the water-dispersible blocked isocyanate as described in the above-mentioned Japanese Laid-Open Patent Application Nos. Sho 61-31422 and Hei 4-159260.